This invention relates generally to parcel sortation systems and, more particularly, to systems which discharge parcels individually supported on transport units to selected receiving ports. The transport units have individual carrier belts, which are operable perpendicular to the conveying path of unit movement in order to discharge the parcel to the selected destination port.
Crossbelt sortation systems are known for their ability to handle parcels of widely varying characteristics. For example, such systems may be used to sort magazines or envelopes at a postal center, frozen food articles, cellophane-wrapped clothing articles, or the like. Crossbelt sortation systems are so widely adaptable because the parcels are loaded onto carrier belts, moveable on transport units orthogonally of the conveying path of the parcels, and discharged from the transport units with the assistance of the carrier belts. In addition to accommodating parcels of varying characteristics, crossbelt sortation systems are capable of being compact because they are able to discharge parcels to closely spaced receiving ports on both sides of the conveying path. Furthermore, parcels may be inducted to the transport units at various separate locations using a plurality of induction stations.
Crossbelt sortation systems are not without their difficulties. Although such systems have been capable of handling parcels of varying characteristics, the size of the handled parcels has been limited by the dimensions of the upper surface of the carrier belt, the induction belt width, and the receiving port width. Therefore, in order to handle larger packages, it has been necessary to increase the size of the transport units, the induction belts, and the receiving ports. This results in a direct increase in system cost and operating expense. Importantly, it is in direct conflict with the goal of providing a compact system.
Another difficultly with crossbelt sortation systems is the relative complexity of the series of transport units, which units creates the need for a constant monitoring of the transport units in order to determine when a unit is not properly functioning. In order to determine that a transport unit is not functioning, it is known to mount magnets to the drive pulley or idle pulley supporting the carrier belt of each transport unit. As an non-loaded transport unit passes a carrier station, a command is given to the transport unit to operate the belt according to a known velocity profile. A stationary-mounted pickup coil receives an induced voltage from the rotating magnets and control circuitry converts the induced voltage into a speed signal. However, the voltage induced in the pickup coil is sensitive to the speed of magnet movement as well as the distance between the magnet and the coil. Accordingly, such systems are not always reliable and require frequent calibration in order to ensure operability.